This invention relates generally to the production of composite metal tubes having laminated multiple walls and used for piping in chemical and other plants, as oil and gas well tubing, for oil and gas pipelines, and like pipes.
Among the multiple-wall composite tubes of the character referred to above and known heretofore for transporting fluids such as those containing corrosive substances, there are double-wall pipes in each of which the inner pipe or liner tube is made of a corrosion-resistant material for effective conducting of corrosive fluid, while the outer pipe is designed to provide strength to withstand internal pressures and external forces. For example, there is a double-wall pipe comprising a stainless-steel inner pipe and a carbon-steel outer pipe in which the inner pipe is fitted.
Among the known methods of producing such composite pipes, the shrink-fit method and other tube heating and expanding methods have been developed. In a known method disclosed in U.S. Pat. No. 3,064,344 to Arne, the inner pipe is inserted into the outer pipe and expanded into contact with the inner surface of the outer pipe, and then the outer pipe is heated, the outer pipe thereafter being cooled and shrunk thereby to obtain a tight or interference fit between the two pipes.
In this method, when the inner pipe is expanded into contact with the inner surface of the outer pipe, the two pipes are brought into tight heat transferring relationship so that even if the outer pipe is heated thereafter for thermal expansion thereof, a substantial temperature difference cannot be established between the outer and inner pipes. This means that the method is difficult to put into practice. Therefore, in order to enable establishment of a substantial temperature difference between the pipes, it is necessary to provide a clearance between the pipes before the heating of the outer pipe is carried out.
Furthermore, according to this method, a considerably large-scale heating device comprising a large number of heating elements or the like must be provided on the outer side of the outer tube, whereby the required equipment becomes disadvantageously large and expensive. Another difficulty arises in the case of tubes of long length in that the weight of the apparatus and equipment becomes great, whereby the operation and maintenance thereof become troublesome.